Beam guidance insert for a source chamber of an EUV radiation source

Abstract

A beam guidance insert (25) for a source chamber of an EUV radiation source has a sleeve-shaped base body (26), a beam inlet opening (27), and a beam outlet opening (28). A guidance channel (29) widens in the base body (26) from the beam inlet opening (27) to the beam outlet opening (28) to guide EUV radiation (5) emanating from a source region of the EUV radiation source. The guidance channel (29) widens from the beam inlet opening (27) to the beam outlet opening (28) with a half-opening angle of at least 2.0 degrees. This results in a beam guidance insert that enables an increased EUV radiation flux through the guidance channel, which in turn makes it possible to increase the inspection speed of a metrology system equipped with the beam guidance insert.

Description

[0001] The invention relates to a beam guidance insert for a source chamber of an EUV radiation source. Furthermore, the invention relates to a beam guidance assembly for a radiation source with such a beam guidance insert, an EUV radiation source with such a beam guidance insert or with such a beam guidance assembly, an optical system with such a beam guidance assembly, and a metrology system with such an optical system.

[0002] Such a metrology system or mask inspection system is known from US 10,042,248 B2, DE 102 20 815 A1 and WO 2012 / 101269 A1. A beam guidance insert for a source chamber of an EUV radiation source is known from DE 10 2021 207 565 B3. US 2007 / 0210717 A1 discloses an induction-driven plasma light source.

[0003] It is an object of the present invention to increase the inspection speed of a metrology system.

[0004] This problem is solved according to the invention by a beam guidance insert with the features specified in claim 1.

[0005] According to the invention, it has been recognized that, despite the high demands regularly placed on the negative pressure in a vacuum chamber surrounding the EUV radiation source of a metrology system, it is possible to significantly increase the opening angle of a guide channel in a base body of the beam guidance insert. This results in a higher throughput of EUV radiation through the beam guidance insert compared to the prior art. Accordingly, it is possible within the metrology system, whose EUV radiation source is equipped with such a beam guidance insert, to direct more useful EUV radiation to an object field of interest within the metrology system. A correspondingly higher inspection speed of the metrology system is the result.

[0006] The opening angle of the guide channel is twice the angle between the generatrix extending between the beam inlet and outlet openings, on the one hand, and a central longitudinal axis of the guide channel, on the other. Similarly, half the opening angle is the angle between the respective generatrix and the central longitudinal axis. If the guide channel is conical due to a corresponding design of the base body or the beam guidance insert, the opening angle is twice the angle between the corresponding cone generatrix and the central longitudinal axis of the guide channel.

[0007] The opening angle can be an angle between a first line and a second line. The first line can pass through a first ray entry point and a first ray exit point of a first cross-sectional surface when cutting through the base body from the ray entry aperture to the ray exit aperture. The second line can pass through a second ray entry point and a second ray exit point of a second cross-sectional surface when cutting through the base body from the ray entry aperture to the ray exit aperture. The first ray entry point and the second ray entry point can be points of the ray entry aperture that lie on the first cross-sectional surface and on the second cross-sectional surface, respectively, and are closest to each other. The first ray exit point and the second ray exit point can be points of the ray exit aperture that lie on the first cross-sectional surface and on the second cross-sectional surface, respectively.lie on the second cut surface and are closest to each other.

[0008] The guide channel can be widened from the beam inlet to the beam outlet such that it widens in at least one section in the direction from the beam inlet to the beam outlet. The guide channel can be widened from the beam inlet to the beam outlet such that the beam inlet is smaller than the beam outlet. The guide channel can be widened from the beam inlet to the beam outlet such that a cross-section of the guide channel increases at least partially continuously from the beam inlet to the beam outlet. Alternatively or additionally, the guide channel can be widened from the beam inlet to the beam outlet such that a cross-section of the guide channel increases at least partially in steps from the beam inlet to the beam outlet.The guide channel can be at least partially widened in the form of a circular conoid from the beam inlet to the beam outlet. The guide channel can be at least partially widened conically from the beam inlet to the beam outlet. The guide channel can also have at least one section with a cylindrical geometry between the beam inlet and the beam outlet. The guide channel can also have at least one section between the beam inlet and the beam outlet that widens in the direction from the beam outlet to the beam inlet.

[0009] The main body of the beam guidance insert is sleeve-shaped, meaning it completely encloses a through-channel, which in turn provides a guide channel for the EUV radiation to be guided. Any profiling or contour of the channel cross-section, as well as any external profiling or contour of the main body, can be adapted to beam guidance requirements on the one hand and structural requirements on the other.

[0010] Half the opening angle of the guide channel in the base body of the beam guidance insert can be at least 3 degrees, at least 4 degrees, or at least 5 degrees. This half opening angle is regularly less than 25 degrees.

[0011] The beam guiding insert can be part of an illumination optic for directing useful radiation towards an object field. In particular, a photomask can be illuminated as the object using such an optical system. The photomask can have an aspect ratio between 1:1 and 1:3, preferably between 1:1 and 1:2, and most preferably 1:1 or 1:2. The photomask can be substantially rectangular. The photomask can preferably be 5 to 7 inches (1 inch = 2.54 cm) long and wide, and more preferably 6 inches long and wide. Alternatively, the photomask can be 5 to 7 inches long and 10 to 14 inches wide, and more preferably 6 inches long and 12 inches wide.

[0012] The beam inlet and beam outlet openings of the beam guide insert are each elliptical in design.

[0013] Such an elliptical design of the beam entry and exit apertures has proven effective in practice. In particular, it allows for the provision of a corresponding elliptical illumination pupil for illuminating the object field of the metrology system. This elliptical illumination pupil can be matched to a corresponding elliptical illumination pupil of a projection exposure unit, which is used in production processes employing a lithography mask to be inspected by the metrology system. Object field illumination by the metrology system can then be well-matched to the ambient lighting in the projection exposure unit, thus improving the inspection results of the metrology system. The opening or sleeve wall of the beam guide insert between the beam entry and exit apertures can be conical or frustoconical in longitudinal section.The beam guidance insert can therefore have, in particular, an elliptical-conical geometry.

[0014] As an alternative to an elliptical design for both the beam inlet and outlet openings, only one of these openings can be elliptical, while the other is circular, for example. Depending on the design of the beam guidance insert, only the beam inlet, only the beam outlet, or only a cross-section of the guide channel parallel to the beam inlet or outlet opening can be elliptical.

[0015] The beam inlet opening and / or the beam outlet opening and / or a cross-section lying parallel to the beam inlet opening or the beam outlet opening can, for example, be circular.

[0016] The aspect ratio between a long and short semi-axis of an ellipse describing the elliptical design of the beam entry guide and the beam exit aperture is at least 1.2.

[0017] Such an aspect ratio is well suited to the lighting requirements of a metrology system equipped with the beam-guiding insert. The aspect ratio can be at least 1.3, at least 1.5, or at least 2. Typically, the aspect ratio is less than 5.

[0018] In particular, when the guide channel has an opening aspect ratio of the beam inlet aperture and / or the beam outlet aperture of at least 1.2, the guide channel can have a varying opening angle in the circumferential direction around the openings, which lies in the range between a smallest half opening angle and a largest half opening angle.

[0019] A maximum half-opening angle of the guide channel of the base body of the beam guidance insert according to claim 2 results in a correspondingly high throughput for the EUV useful light. The maximum half-opening angle can be at least 3 degrees, at least 4 degrees, at least 5 degrees, at least 6 degrees, at least 8 degrees, and can also be at least 10 degrees.

[0020] The advantages of a beam guidance assembly according to claim 3 correspond to those already explained above with reference to the beam guidance insert. The filter can additionally be designed to improve the effective pumping capacity of a vacuum pump for pumping a gas flow through the guide channel in the base body of the beam guidance insert.

[0021] The filter distance can be greater than 10% of the collector distance, so that the filter does not undesirably obstruct a gas flow through the jet guide insert.

[0022] The filter can be designed in such a way that a sub-chamber of an optical system containing the beam guidance insert is isolated from a sub-chamber containing the collector by means of the filter.

[0023] A filter spacing according to claim 4 has proven particularly effective in suppressing unwanted gas flow downstream of the beam guide insert. The ratio between the filter spacing and the collector spacing can be at most 40%, 30%, 25%, or even 20%. Typically, this ratio is greater than 10%. Such a minimum spacing prevents unwanted obstruction of gas flow by the beam guide insert and also prevents unwanted debris deposition on the filter.

[0024] The advantages of an EUV radiation source according to claim 5 correspond to those already explained in the preceding context with regard to the beam guidance insert and also with regard to the beam guidance assembly.

[0025] The same applies to the advantages of an optical system according to claim 6.

[0026] An imaging optic according to claim 7 can be adapted to an increased EUV useful light throughput, for example by a correspondingly good correction of imaging errors of a comparatively large object field, for example an object field whose area is greater than 0.01 mm. 2 The object field can, in particular, have an extent in the range between 0.02 mm. 2 and 0.2 mm 2 exhibit. The area of ​​the object field can be, for example, 0.12 mm. 2 lay.

[0027] The advantages of a metrology system according to claim 8 correspond to those already explained above with reference to the optical system. The object holder is, in particular, an object holder for scanning, especially for line-by-line scanning, the displacement of the object to be examined. The detector can be a CCD or a CMOS detector.

[0028] A vacuum pump can be part of the metrology system to create a vacuum in a vacuum chamber. The vacuum pump can have multiple pumping stages. The vacuum chamber can be divided into several compartments, each emptied by a pump of its respective pumping stage. This allows for precise control of the gas flow and, particularly in the area of ​​sensitive optics within the metrology system, results in improved vacuum purity.

[0029] The metrology or inspection system can be a system for actinic mask or wafer inspection.

[0030] An embodiment of the invention is explained in more detail below with reference to the drawing. This drawing shows: Fig. 1 schematically in a meridional section a mask inspection system for lithography masks for use with EUV illumination light with an illumination system comprising an energy detection assembly with a beam homogenizing element and with at least one EUV energy sensor device; Fig. 2 a beam guidance insert for a source chamber of an EUV radiation source of the mask inspection system, seen from above with a view towards the direction of the beam of the EUV illumination light emanating from the source chamber; Fig. 3 a cut according to line III-III in Fig. 2; Fig. 4 a cut along line IV-IV in Fig. 2

[0031] An illumination optic 1 is part of an optical system 2 of a mask inspection system 2a for use with EUV illumination light 3. A beam path of the illumination light 3 is in the Fig. Figure 1 illustrates the illumination optics 1 via marginal rays and a main ray. The illumination light 3 illuminates an object field or illumination field 4 of the mask inspection system 2a. The mask inspection system 2a is also referred to as a metrology system.

[0032] The illumination 3 is generated by an EUV light source 5 in a source area 6. The light source 5 can generate EUV useful radiation in a wavelength range between 2 nm and 30 nm, for example in the range between 2.3 nm and 4.4 nm or in the range between 5 nm and 30 nm, for example at 13.5 nm.

[0033] Light source 5 is designed as a plasma light source. This could be, for example, a laser-produced plasma (LPP) source or a discharge-produced plasma (DPP) source. Such plasma sources are generally known as light sources for EUV projection systems. The pulse frequency of light source 5 can be in the kHz range.

[0034] To facilitate spatial relationships, a Cartesian xyz coordinate system is used below. The x-axis is perpendicular to the drawing plane. Fig. 1 and runs into it. The y-axis runs in the Fig. 1 horizontally to the left and the z-axis runs in the Fig. 1 vertically upwards.

[0035] After emission by the light source 5, the illumination light 3 first passes through a useful light filter 8, which is positioned in an operating position in the beam path of the illumination light 3 between the source volume 6 and a first ellipsoidal mirror IL1 of the illumination optics 1. The useful light filter 8 can be one of a plurality of filters, which, for example, in the metrology system 2a, are stored in a filter magazine. Another useful light filter can be positioned in a standby position outside the illumination light beam path of the illumination optics 1. The useful light filters 8 can have the same transmission characteristics, and a change between the useful light filters can then be made if a degradation of the filtering effect of the operating useful light filter 8 is detected.Alternatively, the useful light filters can also have different filter characteristics and, for example, allow different useful light wavelength ranges to pass through into the subsequent illumination light beam path or be optimized to filter out different proportions of false light.

[0036] The useful light filters can be designed in such a way that they filter out, in particular, pump light carried along in the illumination light beam path, which was used in the source volume 6 for useful light generation.

[0037] After passing through filter 8 and mirror IL1, the illumination light 3 first passes through an aperture diaphragm 9, which limits the beam of the illumination light 3 at its edges. Following this, the illumination light beam 3 is directed towards a beam homogenizing element 11 of the illumination optics 1. Mirror IL1 serves as a coupling optic 10 for coupling the illumination light 3 into the beam homogenizing element 11. The beam homogenizing element 11 can be a mixed optic with at least one, and for example, two faceted mirrors arranged downstream of each other in the beam path of the EUV illumination light 3. Alternatively or additionally, the beam homogenizing element 11 can be designed as a hollow waveguide.

[0038] Between the source volume 6 and the beam homogenizing element 11, typically after the first mirror IL1 of the illumination optics 1, the illumination light 3 passes through an opening in a wall of a vacuum chamber VK, which is located in the Fig. 1 is indicated in the illumination light beam path between the mirror IL1 and the illumination light aperture diaphragm 9.

[0039] The aperture diaphragm 9 enables a controlled gas flow between the source chamber or vacuum chamber VK and a subsequent, also evacuated, chamber of the mask inspection system 2a. The aperture diaphragm 9 also limits the numerical aperture of the illumination beam 3 emitted from the source area 6 to a value between 0.02 and 0.2, for example, between 0.07 and 0.15 or between 0.05 and 0.08. Alternatively or additionally to the aperture diaphragm 9, an aperture-limiting diaphragm can be arranged between the beam homogenizing element 11 and a subsequent optical component of the illumination optics 1, as shown in the Fig. 1 is indicated in 9a. It is also possible to arrange such a further aperture stop in the beam path of the illumination light 3 after the beam homogenizing element 11 between two downstream optical components of the illumination optics 1.

[0040] The ellipsoidal mirror IL1 serves to image the source region 6 of the EUV light source 5 into an entrance aperture 12 in an entrance plane 13 of the beam homogenizing element 11. A first focal point of the ellipsoidal mirror IL1 is thus located in the source region 6, and a second focal point of the ellipsoidal mirror IL1 is located in the entrance aperture 12. The ellipsoidal mirror IL1 focuses the illumination beam 3 into the entrance aperture 12 in the entrance plane 13 of the beam homogenizing element 11. The entrance-side numerical aperture of the illumination beam 3 at the entrance aperture 12 can be in the range of 0.02 to 0.2, for example, in the range of 0.05.

[0041] The angle of incidence of a central main ray of the illumination beam 3 on the coupling mirror IL1 can be in the range between 10° and 20°. The ellipsoidal mirror IL1 can be a normal incidence (NI) mirror, but can also be configured as a grazing incidence (GI) mirror.

[0042] The inlet opening 12 and an outlet opening 14 of the beam homogenizing element 11 are each square or rectangular with typical dimensions in the range of 0.5 mm to 5 mm, and, for example, between 0.5 mm and 2 mm, or between 0.5 mm and 1 mm. The aspect ratio of the inlet opening 12 and an equally sized outlet opening 14 of the beam homogenizing element 11 for the illuminating light 3 in an exit plane 15 is between 0.5 and 2. Typical sizes of the inlet opening 12 and the outlet opening 14 of the beam homogenizing element 11 are, for example, 0.5 mm x 1.0 mm, 0.75 mm x 0.75 mm, 1.0 mm x 2.0 mm, or 1.5 mm x 2.0 mm.

[0043] The beam homogenizing element 11 has a typical length perpendicular to the planes 13 and 15, i.e. along a principal beam direction of the illumination light 3, in the range between 50 mm and 500 mm, e.g. in the range between 50 mm and 150 mm, in particular in the range between 50 mm and 100 mm.

[0044] An angle between a normal to the entrance plane 13 of the beam homogenizing element 11 and the main beam of the illumination beam 3 incident into the entrance aperture 12 can be 0° or alternatively can be different from 0° and, for example, be in the range between 0° and 1.5°, for example between 0.25° and 0.75° and especially in the range of 0.5°.

[0045] A ratio of the distance between the inlet plane 13 and the outlet plane 15, and a size or typical diameter of the inlet opening or outlet opening 12, 14, lies in the range between 50 and 1000 and can, for example, lie in the range between 50 and 200.

[0046] A downstream imaging output coupler optic 16 with two mirrors IL2, IL3, located after the beam homogenizing element 11, images the exit aperture 14 of the beam homogenizing element 11, which lies in an exit plane 15, into the illumination field 4 in an object plane 17. The image-side numerical aperture of this imaging can be in the range of 0.05 to 0.2.

[0047] In the illustrated embodiment, the output coupling mirror optic 16 has exactly two mirrors, namely mirrors IL2 and IL3. The aperture diaphragm described above, which may be used after the beam homogenizing element 11, can be arranged between the beam homogenizing element 11 and mirror IL2 or between mirrors IL2 and IL3.

[0048] The output coupler 16 is designed in the manner of a Wolter telescope, specifically a Wolter optic of type I. Such Wolter optics are described in J.D. Mangus and J.H. Underwood, "Optical Design of a Glancing Incidence X-ray Telescope," Applied Optics, Vol. 8, 1969, page 95, and the references cited therein. A hyperboloid can also be used in such Wolter optics instead of a paraboloid. Such a combination of an ellipsoidal mirror with a hyperboloid mirror also constitutes a Wolter optic of type I.

[0049] An embodiment of the output coupling mirror optics 16 is described in US 10,042,248 B2.

[0050] The imaging factor β1 of the input-coupling mirror optics 10 can range from 0.1 to 50, meaning it can reduce the image by a factor of 10 to magnify it by a factor of 50. The imaging factor β2 of the output-coupling mirror optics 16 can range from 0.02 to 10, meaning it can itself reduce the image by a factor of 50 to magnify it by a factor of 1. The product β1, β2 of the two imaging factors in the illumination optics 1 can range from 0.25 to 10.

[0051] In the object plane 17, a reticle 18 to be inspected is arranged as the object or mask to be inspected, and is held by a reticle holder 19. The object 18 can be configured as a photomask. The photomask 18 can have an aspect ratio between 1:1 and 1:3, preferably between 1:1 and 1:2, and particularly preferably 1:1 or 1:2. The photomask 18 can be substantially rectangular. The photomask 18 can preferably be 5 to 7 inches (1 inch = 2.54 cm) long and wide, and particularly preferably 6 inches long and wide. Alternatively, the photomask 18 can be 5 to 7 inches long and 10 to 14 inches wide, and preferably 6 inches long and 12 inches wide.

[0052] The reticle holder 19 is mechanically connected to a reticle displacement drive 20, via which the reticle 18 is displaced along an object displacement direction y during a mask inspection. This enables scanning displacement of the reticle 18 in the object plane 17.

[0053] The illumination field 4 has a typical dimension in the object plane 17 that is less than 0.5 mm. In the illustrated embodiment, the extent of the illumination field 4 is 0.5 mm in the x-direction and 0.5 mm in the y-direction.

[0054] The x / y aspect ratio of the illumination field 4 matches the x / y aspect ratio of the exit aperture 14.

[0055] The illumination field 4, or a part of the illumination field 4 which then represents an object field, is projected by a projection optic PO onto an image field 21 in an image plane 22. The image field 21 can have a size in the range of 150 mm x 250 mm. The shorter image field extent runs along the scan direction y.

[0056] The projection optics PO have numbered mirrors M1 and M2 in the imaging beam path, thus comprising a total of two mirrors. Depending on the design of the projection optics PO, the number of mirrors can also be greater than two. An aperture diaphragm 9b is arranged in an entrance pupil plane EP of the projection optics PO, which lies in the imaging beam path of the illumination / imaging light between the reflecting reticle 18 and the first mirror M1. This aperture diaphragm 9b can also serve to define any internal obscuration of the projection optics PO.

[0057] The mirrors M1 and M2 of the projection optics PO are designed as NI mirrors with an angle of incidence of the illumination and imaging light 3 of less than 45°.

[0058] An illumination light beam path of illumination light 3 for illuminating reticulum 18 and an imaging light beam path of projection optics PO for imaging the object field 4 onto the image field 21 intersect in a crossing area. This crossing area lies in the region of the entrance pupil plane EP of projection optics PO. The imaging light beam path intersects here with the illumination light beam path between the exit aperture 14 and the mirror IL2 of illumination optics 1, as well as between the mirrors IL2 and IL3 of illumination optics 1.

[0059] As an alternative to the depicted two-mirror configuration of the projection optic PO, the number of mirrors in the projection optic PO can also be greater than 2 and can be, for example, 4 or 6. The object field 4 has a length of approximately 400 µm along the x-coordinate and approximately 300 µm along the y-coordinate.

[0060] The image field 21 is acquired by a detection device 23, e.g., by one or more CCD or CMOS cameras. For details of the imaging into the image field, reference is made to US 10,042,248 B2 and the references given in US 10,042,248 B2. The detection device 23 can also be implemented as a TDI (time delay integration) detection device with a plurality of TDI detectors. Such an implementation is explained in more detail below.

[0061] The mask inspection system 2a enables, for example, the inspection of a structure on reticulum 18. For this purpose, reticulum 18 can be scanned line by line in the xy-plane using the reticulum displacement device 20 until an entire surface of interest on reticulum 18 has been imaged by the projection optic PO of the mask inspection system 2a and inspected accordingly.

[0062] To guide the EUV illumination light 3 in the beam path directly after the source area 6, a beam guiding insert 25 is used in a source chamber of the EUV light source 5, which is otherwise not shown in detail. Details of the beam guiding insert 25 are also described below with reference to the Fig. 2 to 4 explained.

[0063] The beam guiding insert 25 has a sleeve-shaped base body 26. A beam inlet opening 27 of the beam guiding insert 25 serves for the entry of the EUV illumination light 3, i.e., the EUV radiation emanating from the source volume or source area 6. When the beam guiding insert 25 is mounted in the source chamber, the beam inlet opening 27 faces the source volume 6.

[0064] The base body 26 of the beam guidance insert 25 also has a beam exit opening 28 for the exit of the EUV illumination light 3 from the beam guidance insert 25. The beam exit opening 28 is facing away from the source area 6 when the beam guidance insert 25 is mounted.

[0065] A guide channel 29 in the base body 26, which runs from the beam inlet opening 27 to the beam outlet opening 28, has a half opening angle of at least 2.5 degrees.

[0066] The beam inlet 27 and the beam outlet 28 are each elliptical. The ratio of the lengths of the semi-major and semi-minor axes of the ellipses describing the beam inlet 27 and the beam outlet 28, respectively, is 2 in the illustrated embodiment.

[0067] The guide channel 29 has a conical shape between the elliptical beam inlet opening 27 and the comparatively larger, elliptical beam outlet opening 28.

[0068] In the direction of the long semi-axis (cf. the section plane of the Fig. 3) Half the opening angle of the beam guidance channel 29 of the beam guidance insert 25 is 10 degrees. A total opening angle α is therefore 20 degrees. In the plane perpendicular to this, to the left of the short semi-axis of the ellipse (see the section plane of the Fig. 4) Half the opening angle of the guide channel 29 is 5 degrees. A total, full opening angle β is therefore 10 degrees. The guide channel 29 thus has a maximum half opening angle α / 2 of 10 degrees.

[0069] Due to the elliptical apertures 27, 28 and the half-aperture angles α / 2, β / 2, which differ by a factor of 2, a correspondingly elliptical illumination pupil of the input coupling optics 10 is formed, which is transformed via the beam homogenizing element 11 into a corresponding illumination pupil of the output coupling optics 16. This elliptical illumination pupil has a long semi-axis parallel to the x-axis of the Fig. 1 and a short semi-axis in the yz-plane of the Fig. 1. Accordingly, the projection optics PO, with which the object field 4 is mapped into the image field 21, also has an elliptical entrance pupil with an x / y aspect ratio or, in pupil coordinates, a σ. x / σ y-aspect ratio greater than 1, which is 2 in the described embodiment. The projection optics PO can be anamorphic, in which case the elliptical entrance pupil of the projection optics PO is formed into a round exit pupil.

[0070] Due to the comparatively large opening angles α and β of the beam guidance channel 29 of the beam guidance insert 25, a high luminous flux of the EUV illumination light 3 results between the source area 6 and the object field 4.

[0071] Despite the elliptical illumination pupils, the coupling optics 10 results in a source image at the entrance aperture 12 in the entrance plane 13, which has an aspect ratio of approximately one in the entrance plane 13. Therefore, the beam homogenizing element 11 does not need to be adjusted with respect to the aspect ratio of the apertures 12, 14 when transitioning from a conventional beam guide insert with the same aperture angles α, β to the beam guide insert 25 with an aspect ratio α / β ≠ 1.

[0072] The base body 26 also has a flange section 26a for mounting the beam guidance insert 25 in a corresponding receptacle of the source chamber.

[0073] Both the outer sleeve wall 30 of the base body 26 and the flange section 26a have a circular outer diameter.

[0074] In the beam path of the EUV illumination light 3, the useful light filter 8 is located downstream of the beam guiding insert 25. A filter distance A between the filter 8 and the beam guiding insert 25 is at most 50% of a collector distance B between the collector mirror IL1 and the beam guiding insert 25.

[0075] The mirror IL1 serves as a collector for the EUV illumination light 3 and for transferring the EUV illumination light 3 emanating from the source area 6 and guided by the guide channel 29 into an intermediate focus in the entrance plane 13. The EUV collector IL1 thus serves to collect the EUV illumination light 3 exiting from the beam guide insert 25 and passing through the useful light filter 8.

[0076] The mask inspection system 2a also has a vacuum pump 32 for generating a negative pressure in the vacuum chamber VK.

[0077] Since the inlet opening 27 has a significantly smaller opening area compared to the outlet opening 28, the gas flow from the source region 6 of the beam path of the EUV illumination light 3 through the guide channel 29 is comparatively low and can be pumped out by the vacuum pump 32 so that a sufficient negative pressure prevails within the vacuum chamber VK. Undesired absorption of EUV useful light by gas remaining in the vacuum chamber VK is thus reduced.

[0078] Xenon may be present as a residual gas in the vacuum chamber VK. The partial pressure of xenon in the vacuum chamber VK is less than 10 -3 mbar. This results in a desired low residual absorption of the EUV illumination light 3.

[0079] The pumping capacity of the vacuum pump 32 is in particular greater than 500 1 / s or greater than 1000 1 / s, for example greater than 2000 1 / s.

[0080] In the area between the wavelength filter 8 and the beam guide insert 25, the vacuum chamber VK can have a sub-chamber that is pumped out by its own pump stage of a pumping system, which also includes the vacuum pump 32. By means of such a differential pump stage, both before and after the filter 8, the vacuum purity in the area of ​​the vacuum chamber VK downstream of the filter 8 is improved, thus preventing unwanted deposition of debris on the mirror IL1.

Claims

[1] Beam guidance insert (25) for a source chamber of an EUV radiation source (5) of a metrology system, - with a sleeve-shaped base body (26) - with a beam inlet opening (27) for the entry of EUV radiation (5) emanating from a source area (6) of the EUV radiation source (5), wherein the beam inlet opening (27) is facing the source area (6) when the beam guidance insert (25) is mounted, - with a beam exit opening (28) for the exit of the EUV radiation (3), which, when the beam guidance insert (25) is mounted, is directed away from the source area (6), - wherein a guide channel (29) in the base body (26) widens from the beam inlet opening (27) to the beam outlet opening (28) with a half opening angle (α / 2, β / 2) which is at least 2.0 degrees. - wherein the beam inlet aperture (27) and the beam outlet aperture (28) are each elliptical in shape, and - wherein an aspect ratio between a long and a short semi-axis of an ellipse describing the elliptical design of the ray inlet aperture (27) and the ray outlet aperture (28) is at least 1.

2. [2] Beam guidance insert according to claim 1, characterized by , that a largest half opening angle (α) of the guide channel (29) is at least 2.5 degrees. [3] Beam guidance assembly (25, 8, IL1) for an EUV radiation source (5), - with a beam guidance insert (25) according to one of claims 1 or 2 - with a filter (8) downstream of the beam guidance insert (25) in the beam path of the EUV radiation (3) for separating EUV useful radiation (3) from radiation whose wavelength differs from that of the EUV useful radiation (3), - with an EUV collector (IL1) for collecting the EUV useful radiation (3) exiting the beam guidance insert (25) and passing through the filter (8). [4] Beam guidance assembly according to claim 3, characterized by , that a filter distance (A) between the filter (8) and the beam guidance insert (25) is at most 25% of a collector distance (B) between the collector (IL1) and the beam guidance insert (25). [5] EUV radiation source (5) with a beam guidance insert (25) according to one of claims 1 or 2 or with a beam guidance assembly according to claim 3 or 4. [6] Optical system - with a beam guidance assembly according to claim 3 or 4 and - with a lighting optic (11, IL2, IL3) for guiding the EUV useful radiation (3) from the collector (IL1) to an object field (4). [7] Optical system according to claim 6, characterized by an imaging optic (PO) for imaging the object field (4) into an image field (21). [8] Metrology system - with an optical system according to claim 6 or 7, - with an object holder (19) for holding an object (18) to be examined in the object field (4), - with a detector (23) arranged in the image field (21).

Images